Methods of curing vulcanizable compounds



March 27, 1956 G. E. HENNING METHODS OF CURING VULCANIZABLE COMPOUNDS Filed Feb. 8, 1952 lNVENTOR G. E. HENN/NG BY ATTORNEY Unite METHODS OF CURING VULCANIZABLE COMPOUNDS George E. Henning, Baltimore, Md., assignor to Western Electric Company, Incorporated, New York, N. Y., a

corporation of New York Application February 8, 1952, Serial No. 270,593

Claims. (Cl. 1853) This invention pertains to methods of curing vuclanizable compounds, and more particularly to methods of curing vulcanizable compounds by dielectric heating.

One of the recent developments pertaining to the curing of vulcanizable compounds is the application of microwave dielectric heating. The use of energy at microwave frequencies facilitates a rapid heating of dielectric material and affords a suitable method for uniformly and rapidly heating and curing continuous lengths of vulcanizable compounds.

The above method is particularly well suited for curing vulcanizable compounds which serve as insulating coverings on continuous lengths of electric conductors. It has been found, however, that in order to produce a tight, Smooth-skinned insulating covering upon a conductor, the

vulcanizable compound must be confined and subjected to pressure during the curing operation.

Various means have been suggested to fulfill the above requirements. These means have not proved entirely satisfactory when applied to vulcanization processes utilizing microwave dielectric heating because of the problems peculiar to this type of heating. At the present stage. of development, microwave dielectric heating applications are sharply restricted by the limitation in the available sources of microwave frequency power. Any commercially feasible process involving microwave frequencies must have a minimum of energy losses.

It is an object of this invention to provide new and improved methods of curing vulcanizable compounds.

It is another object of this invention to provide new and improved methods of curing vulcanizable compounds" by dielectric heating.

Other objects of this invention will become apparent as the specification proceeds.

In one method illustrating certain features of this invention, a conductor is covered with an extruded layer of uncured vulcanizable insulating compound. The insulated conductor is then provided with a sheath of dielectric material which has substantially lower dielectric losses than that of the insulating covering on the conductor. The

sheathed and insulated conductor is next subjected to a high frequency electric field wherein the vulcanizable insulating compound is cured.

A clear understanding of the invention will be had from the following detailed description of a specific embodi ment thereof, when read in conjunction with the appended drawing, in which:

Fig. l is a schematic view of a microwave frequency dielectric heating apparatus suitable for use in practicing the invention and illustrating one method embodying the invention;

Fig. 2 is a section taken along line 2--2 of Fig. 1, and

Fig. 3 is a section similar to Fig. 2, illustrating how another method embodying the invention may be practiced.

In 'a specific embodiment of the invention a filamentary conductor of indefinite length is covered with an insulating layer 12 of uncured vulcanizable compound, such as a neoprene compound, which has relatively high dites Patefi o 3 electric losses when subjected to a high frequency alternating electric field. The uncured vulcanizable insulating layer 12 is applied to-the conductor 10 by a suitable conventional extruding operation. It is well known that such a vulcanizable layer-"12 of neoprene compound must be cured by the application of heat and pressure in order to produce a high quality covering upon the conductor 10. 1

An outer sheath 14 of a low dielectric loss thermoplastic material, such as high'molecular weight, normally solid polyethylene is extruded over the uncured vulcanizable, layer 12 in a subsequent conventional extruding operation. In this operation the conductor 10 with its uncured vulcanizable layer 12 is enveloped by the outer sheath 14 of polyethylene. The sheathed and insulated-conductor 10 is then advanced through a suitable microwave frequency heating apparatus, which is shown generally at 15.

The microwave'frequency heating apparatus 15 includes a high frequency vgenerator 17, capable of generating energy at microwave frequencies, which is coupled to a.

cylindrical cavity resonator 18 by a wave guide 20. The microwave frequency heating apparatus 15 is similar to apparatus shown and described in Microwaves and Their Possible Use in High Frequency Heating, a pamphlet distributed by Westinghouse Electric Corp, Industrial Electronics Division, Baltimore, Maryland.

The cylindrical cavity resonator 18 is provided with aperturesat both ends which permit the passage of the sheathed and covered conductor therethrough. Within the cavity resonator 18, the advancing sheathed and insulated conductor 10 is subjected to a high frequency electric field which causes a rapid heating of the layer 12, which has high dielectric loss characteristics. The sheathed and covered conductor 10 is advanced at such a rate'thatlthe layer12 reachesfan optimum temperature at 'which the neoprene compound becomes cured during its passage through the cavity resonator 18.

Since the outer'polyethylene sheath 14 has relatively low dielectric losses as compared to the relatively high dielectric losses of the layer12 of neoprene compound, theftempera'ture'of the sheath 14, except for portions thereof adjacent to the layer 12, remains substantially unchanged during the transit of the sheathed and covered conductor 10 through the cavity resonator 18. As a result, the propertiesof the sheath 14 remainsubstantially' mally occur if the compound were cured in an unconfined condition. Inaddition, the sheath 14 prevents surface oxidation which would normally occur on the surface of the neoprene compound layer 12 if it were exposed to the atmosphere at ahigh temperature.

After passing through the cavity resonator 18, the

sheathed and covered conductor 10 is passed through a suitable cooling means, such as a bath of water (not.

shown), to reduce the temperatures of the polyethylene sheath 14 and the layer 12 of neoprene compound. The cooled 'outer sheath '14 of polyethylene then is removed by a suitable stripping device (not shown) leaving the conductor 10 with a smooth, high quality layer 12' of cured neoprene compound substantially free from surface defects, such assponging and oxidation. The polyethylene from the sheath 14, which has'been stripped from Patented Mar. 27 1956 a ms. 1

the insulated conductor lflfis suitable for reuse in the extruder which applies the poiyethyleneaheath *id upon Al ernate-em od ment A-n;-alterr rativ e embodiment of the invention 'is 'illustratedinFigl '3 ofthe drawing. Injhis embodiment, a conductor 110 is provided .with an insulating covering 111 of polyethylene, which, is extruded thereupon by conventional means. A jacket lli of uncured neoprene compound is extruded over the polyethylene covering y a subsegucnt conven i na ex ruding ope ation- .45 sheath 114 oflpolyethyleneis applied upon thejaclgeted u 'tinsulated conductcrllllza in,thepreferredcmbod merit.

The .cond tori 'm, with .theiu ulat ng cq erinsilll. jacket and shea h 1.14ttherwnt sadranc dhysn .able mea s hro g hermnanm v ty1842i the d electric h ating apparatu 1.5 where i i subject d t a mi ro v ifr guency alternating electrictfi ldrDHXiDB the trans t .throughhtherrcsonaut ca y .18 suflicient is allowed for the layer 114 of neoprene .vqqmpoundrto bec me Lheated and cured :Howcve a previou ly 41.- scrib th .rzclycthy. nc i sulat ng veri g ,ll kand th p .1x ihy1ene sheath 31.14..arersuhstantial y imaficc ed y heihighjfrq tuencutielddueto the low. dielectric 1 95 veloped within the vulcanizable compounds, such as the neoprene compound, are readily apparent.

What is claimed is:

1. The method of curing vulcanizable compounds, which comprises covering a continuous length of filamentary conductor with .a layer .of an uncured, vulcanizable compound, extruding a sheath of low loss diele tric..,mate ,ia "hav n ielectric l ss s of the order of haracteristics o po yethy ene :Afler cooling, the poly.

ethylene sheath 11.4"is .strioped ifrom sh -.'iusu at d. an a keted condu or 1.10 "and, maybe used assht fiihingjn subsequent oper tions l jifieretofor' standar rm thodslofvcu iug th n oprene commundjukctilfi (cc-- .con inuous cam ulc nizat on) have "caused, so an; i ner, polyethylene n, sulatingrcoyering-rsuoh as-::the covcl'ing11'1. Anymeth 0d. wherein gl ,polyethylenercoyc iu 111 is hea edci unsatislEactory,: .sincei the covering a t nds-1 --bec9mm n noncentric, .therehy de troyin 1th: l nitoun elec rica propertiesofi. hesfinishcdacahlet .I wiilbe -.understood,. hate he urethodsrau tniaterials" utilized in the heretofore described embodiments age merely illustrative, iltnissrnanitest that variqusamct ods utilizing various materials may ih rpracticc wi bin vth s op of the inventioniFortexamp ciz a neoprene; compound has been chosen asrrepresentatiye of-=NuXcaniZahIecemnQunds,whichirnay be:.cured -insaccordanoet with the. teachings of. this" inven tion. Other suitable .compounds,-such as those contain ing rubber, Hana-S la rubbery copolymer of l butadi'ene and styrene) or r the like, may beused insteadof theneoprenecompound.

Also, 'polyethylene'hasheenselected ,as a compound representative of low d ielectiic"lo ss compounds. QQther materia shsuch po ystyrene, ,ohtheiikc, whic mums dielec ric: ulossscharacter sti snot. he .order .o th s hihited byuolyethyleuc, rare.:;sui.tahl 'rna erialsi for outer sheath. Suchimateri lsrp sscs dicleqtrimnower mlc uizahle materialnisuc ia compounds ofiancor c ei rub er, liuua-siaonthmiik eSioce th -:dielectricscnttrg lossnssdirect v proportiona 011 3 reasons for tl1rra lical s1 ficu9 Al about zrdfi sls lic withinshe-ma erials.tsnshg as polyethylene; M Q L flHQB-fi those of polyethylene over the'layer of vulcanizable com ound a ad ancin t e c t nuou en th s sheathed andcovered conductor continuously thr a microwave frequency alternating electric field epy the vulcanizable compound is heated and cured during its transittherethrough.

2. The method of curing vulcanizable compounds, which comprises covering a continuous length of fila-' mentary conductor with a layer of an uncurved, vulcanizblesomnouudext ud ng? Sh a of low s ,tli lcst material 'havin'gdielectriclosses of the order of tho,s e of dY-ififii l lhfi continuou l n h of sh a ed ari -FW- rscs conduc or cont nuous y through a, mi w v j mqi cn ,ralt ua iu tclc fi e b th v ani sl l build isjeated and curedduring its transit there, hrush,.an .stu pin .theou e heat v s i lesuicmats cl mci t e u a z a e 3. The method of curing vulcanizable materials microwave trcquru r ic ss he t ua whi h wmnt t caterin xa continu u len h o filament r cond cto with a iaysrqfniat u o t e c us s tq quita l rccmrpuwi .o r b r; n en n rubhry ppp rms r ro -hi tatlicne n s n xt u 8th Q ,3, polystyrene over the yulcani zableflayei', vand advanc ng hasantiu wskus o s a d-a 9 I fi9 1 outinuo slylthmus m c w v e mltema ss iect icfisidtwhcrh t r a l l y i e et l uilcau ced au il th heat i st n ial unafiscide i h imc hsd o curing u a a l a er alist dielectriche ina swis com s I u ng c rriculuirgg layenof ;a f naterial of the ,group consisting of polythylueisus Pol en u n fi nt r con t?! applying rajaclget .of materialof the .group consisting of vulcanizable compounds of rubbenlneopreneand rub bery copolymersofbutadiene and styrene over the,; insg1- latingflayen re ttr ding an, outer sheath of a material of he s ouncqn ist ueotp ye y enen p yst rcnwre he-jackete an insul d. qn u ua tsn ie 4 W 5- sulting assembly continuously through a high-frequency lt rna ing slec ri rfic e e th v uiza l tm terial is heated and cured while the insulating, yer and' he: sheathmre suhst ntic n f ted! Flu dsi g the iT vine l o cur n v ca izabl v. u t ia by disiectu lhsat uasuh h m s extr in 19 a iisi-l rem a mori o fl swu wastin $1 ,613"

thy t-audrpoly t r n v cfi mn Y wi de t?! r lv uaiiack eo m ria p th swa con stinas uulsuiizehl t qu pquuds o r bb neopr ndT rubb copolymers of butadiene and styrene ov er the in ess? cumulus/ shra o om te ic i t s twp onsist n sc iiz lr th lcn and Poly yr ,-9 fibe ise sete sau insu te TQQ FQUQ F an tr ce vs resulting assembly continuously through a high tret iugi gy lternatin slce -ri xfid whe eb ih yulsen eh swh i hsa hcare:suhstautia lr una ecte isiensnce Cited i th fi 9 hi rpet m QUE-H93 3; ST ATE 3A1" ENT fi 'r o rth zsmu .r n l ns of m su 

1. THE METHOD OF CURING VULCANIZABLE COMPOUNDS, WHICH COMPRISES COVERING A CONTINUOUS LENGTH OF FILAMENTARY CONDUCTOR WITH A LAYER OF AN UNCURED, VULCANIZABLE COMPOUND, EXTRUDING A SHEATH OF LOW LOSS DIELECTRIC MATERIAL HAVING DIELECTRIC LOSSES OF THE ORDER OF THOSE OF POLYETHYLENE OVER THE LAYER OF VULCANIZABLE COMPOUND, AND ADVANCING THE CONTINUOUS LENGTH OF SHEATHED AND COVERED CONDUCTOR CONTINUOUSLY THROUGH A MICROWAVE FREQUENCY ALTERNATING ELECTRIC FIELD WHEREBY THE VULCANIZABLE COMPOUND IS HEATED AND CURED DURING ITS TRANSIT THERETHROUGH. 